"This will be enough to activate Marc Savard when he's ready to play," Chiarelli said during a conference call to announce the transaction. Savard, who has been dealing with post-concussion syndrome, hasn't played yet this season.

There's still no specific timetable when Savard will be able to return, but Chiarelli monitored the forward during Monday's practice and said while there's nothing "definitive" at this time, he had to ramp up his efforts to clear space because of Savard's progress. Chiarelli added that Savard is "on the eve of his return."

It was no secret the Bruins were up against the cap, and Chiarelli has admitted as much, knowing he would have to make some room. Hunwick became the odd man out.

"This was one of the steps that I had to take, that we had to take as an organization, to take care of the cap situation in order to get a player or two back," Chiarelli said. "I do this, recognizing that it's a reality and had to be done."

Chiarelli said the process of deciding on a move wasn't fun, and added the organization is confident in its group of young defensemen. So that meant moving Hunwick made the most sense.

With Hunwick gone, the Bruins will stick with a six-man blue line for now, with Adam McQuaid the No. 6 defenseman. Cohen will be assigned to Providence.

In a phone conversation, Hunwick told ESPNBoston.com he understands the situation, but will miss Boston.

"It's tough. It's disappointing leaving the team I was drafted by, and the team I've spent my entire time as a pro," he said. "But at the same time, it's a new opportunity and I'm excited to have that chance."

Hunwick will be on a plane early Tuesday morning to Colorado, and he's expecting to be in the lineup for the Avalanche against the St. Louis Blues on Tuesday night.

The Bruins drafted Hunwick with their sixth pick (224th overall) in the 2004 draft. The former University of Michigan star began his pro career with Boston's AHL affiliate at Providence in 2007-2008, and also made his NHL debut that season.

"It's an Original Six team with great fans," he said. "I grew up watching the Bruins. Growing up in Michigan I had a chance to watch the Bruins on 'Hockey Night in Canada,' and from the time I was drafted until today, I've loved every minute of being a part of this organization.

"It's been great. The city is phenomenal and I love living downtown. It's been a great experience overall, and that's what makes it so disappointing."

Chiarelli spoke with Hunwick after the trade was made and thanked him for his hard work and professionalism. The GM explained the nature of the business, and that it was difficult to trade a player who was scouted, drafted, signed and developed as a Bruin.

"Matt's a good kid, and generally a quiet kid. I think I detected some shock, and he was very thankful for the opportunity," Chiarelli said. "That's not surprising because he's a real polite and professional kid."

Hunwick has appeared in 164 career NHL games, all with the Bruins, with 13 goals and 32 assists. This season, Hunwick skated in 22 games and registered one goal, two assists and nine penalty minutes.

Cohen, 21, is a first-year pro out of Boston University. The 6-foot-2, 200-pounder possesses a big right-handed shot.

"We've tracked him for a while," Chiarelli said. "He's been on our interest list for a while, as far as young defensive prospects."

Cohen starred for the Terriers from 2007 to 2010. When he received a call from Colorado GM Greg Sherman, Cohen admitted he was hoping he would be shipping back to Boston.

"I was praying," he said. "I had a few cities in mind, but I was praying it wasn't Edmonton, and when he said Boston, I was like, 'Wow, this couldn't be any better.'

"I'm sort of lost for words right now because there's not a better place," he said. "I never realized how much I loved it before I left, and I miss Boston in the worst way."

Chiarelli's work isn't complete. Forward Marco Sturm (knee) is also close to returning to game action, and the Bruins' GM will have to get creative again to make salary cap room.

"It's a business and we have to ice the best team we can within the parameters of the CBA," Chiarelli said. "We're going to do that, and we'll continue to do that."